Process for controlling the vulcanization of rubber and similar materials and products obtained thereby



Patented July 14, 1931 TATE PATENT FICE,

SIDNEY I'E. CADWELL, OF LEONIA, NEW JERSEY, ASSIGNOR TO THE NAUGATUCK CHEMICAL COMPANY, NAUGATUCK, CONNECTICUT, A CORPORATION OF CON- NECTICUT PROCESS FOR CONTROLLING THE VULCANIZATION OF RUBBER AND SIMILAR MATERIALS AND PRODUCTS OBTAINED THEREBY No Drawing. Original application filed June 25, 1923, Serial No. 647,757. Divided and this application filed November 1, 1927.

This invention relates to processes for controlling the vulcanization of rubber and similar materials such as balata, gutta percha and synthetic rubber, and products obtained thereby. It is more particularly directed to processes for checking such vulcanization of rubber or the like combined with a vulcanizing agent, a material containing carbon disulphide, zinc or equivalent metal in comb1- nation and an amine or anyone or more of such substances, and causing vulcanization thereafter if desired; and to products obtained thereby.

The principal object of the present invention is to provide a process for checking the vulcanization of rubber which shall be simple and efficient, particularly in causing sure curbing or checking of vulcanizatlon of rubber in any form including latex, cements or solid rubber whether applied to untreated rubber before vulcanization, to rubber containing one or more vulcanizing or other 1ngredients, or to rubber which has been partially or completely vulcamzed wh le permitting easy resumption of vulcanlzatlon, at normal temperature 70 F., or above, say 212 F., or 240286 F., later if desired. Another object of the invention is to provide a series of products resulting from such processes 1n which such control has been exercised and which therefore may be more readily man1pulated in factory processeswithout danger of prevulcanization and wh1ch Wlll result n rubber articles having improved physical characteristics such as better resistance to ageing. The invention accordingly comprises a process for controlling the vulcanization of rubber which includes causing a vulcanizmg ingredient contained in rubber to react with a substance for checking the vulcanizing function of the ingredient and at will treating the rubber with an agent causing vulcanization, and the products obtained thereby.

This application is a division of Serial Number 647,757, filed June 25, 1923, now U. S. Patent No. 1,698,715.

The term agent as herein employed is in- Serial No 230,385.

tended to include both chemical substances and physical forces such as heat.

The term vulcanizing ingredient as employed herein is intended to include a substance which is a component part of any combination or mixture which is capable of vulcanizing rubber.

In accordance with copending application No. 574,780, filed July 13, 1922, continued in applications Nos. 41,875, filed July 6, 1925, 681,066, filed Dec. 17 ,1923, and copending application No. 574,797, filed July 13, 1922, now Patent No. 1,463,7 94, it has been shown that vulcanization at ordinary temperatures, approximately 70 F., occurs when four ingredients, M in combination, an amine, a material comprising sulphur and a material comprising carbon disulphide or carbon oxysulphide are present. (Above the ordinary temperature, say ranging upwards to 212 F. or 240286 F. vulcanization in the presence of these substances occurs at an increased rate.) M represents zinc or mercury in the mercuric state when vulcanization at ordinary temperatures, approximately 70 copper, preferably in the cupric state, arsenic,

preferably in the arsenous state, manganese, preferably in the manganous state and lead preferably in the plumbous state. It has been found in accordance with the present invention that the vulcanization accomplished by the presence of these ingredients may be controlled by controlling the vulcanizing function of any one of the ingredients by treating it, preferably in rubber, with a substance which reacts chemically therewith, preferably without removing the reaction product where solid rubber is em ployed although it may be removed later if desired, and that after such treatment to check the function, the vulcanization may be carried 011 in the presence of the other ingredients by theapplieation of heat or by replacing the ingredientwhich was reacted client. The control of vulcanization in the manner constituting the present invention is particularly important in its action to prevent the premature vulcanization of rubber compounds containing accelerators and other vulcanizing ingredients which vulcanize at ordinary temperatures or slightly above. Taking the process Of vulcanization set forth in Cadwells copending application Sr. No. 441,691, filed Feb. 1, 1921, in which rubber, zinc oxide, sulphur and oxy normal butyl thiocarbonic acid disulphide are combined and the compound so termed subsequently exposed to the vapors oi aniline, constituting the fourth, i. e. amine ingredient, to effect vulcanization, it this compound without exposure to aniline or otheramine be allowed to stand for a period of time at ordinary temperatures vulcanization is apt to occur, due it is believed to the action of the natural amine occurring in the rubber or to casual amine such as aniline picked up from the atmosphere of the factory, either of which may furnish the fourth ingredient required for vulcanization at ordinary temperature. The premature vulcanization occurs for instance in scrap rubber, that is pieces of rub-- ber-usually small pieces-resulting from cutting or other processes for the manufacture of various rubber articles. By the present invention such premature vulcanization is avoided. If the premature vulcanization mentioned occurs it causes a serious loss of money in factory operations. Furthermore if vulcanized rubber is treated by the present process to check further vulcanization of the rubber, it has been found that further vulcanization substantially does not occur and thereby the ageing properties of the rubber are greatly improved. In addition it has been found that the process may be applied to various types of raw rubber to produce a uniformity of vulcanization therein, for example various lots of smoked sheet vulcanize it has been found at varying speeds. By the application of the present process these varying speeds may be changed to a uniform speed. The uniformity of speed of vulcanization is important in that vulcanized articles having a uniform degree of vulcanization may be automatically secured.

For controlling the vulcanization by influencing the action of an amine orother basic nitrogenous matter constituting one oi the tour ii-igredients mentioned above, the aminemay be rendered partially or totally inactive by treating it with an aldehyde of the aliphatic or aromatic series, such as formaldehyde, benzaldehyde, aceta-ldehyde, etc. These substances lower the basicity of the amine or other basic nitrogenous matter present. Where the amine or other basic nitrogenous matter is not one of the four 1ngi'eclients but 1s used for example with zinc in combination and sulphur, the treatment with aldehyde actually increases the activity of the amine.

The substances for controlling the vulcanizing; functions of these various vulcanizing ingredients leave the rubber substantially unchanged physically. The rubber may be employed in various states such at latex, raw rubber, or products intermediate between latex and raw rubber, such as rubber sponge, as set forth in United States patents of Er nest Hopkinson, 1,423,525 and 1,423,526; rubher which has been compounded and is ready for vulcanization and partially or fully vulcanized rubber. The treatment with the various materials mentioned above may be accomplished'in various ways, such as by mixmg mechanically with the rubber either by milling or similar processor by stirring in latex or cement. Or the various substances either in the gaseous, liquid or solid state may be absorbed by latex, raw rubber, rubber sponge, cements or vulcanized or vul'canizing rubber. i

As an illustration of one embodiment of the invention, 1.0 part of benzaldehyde is combined with 100 parts of rubber, 2 parts of zinc oxide, 2 parts of sulphur and 2 parts of oxy normal butyl thi'ocarbonic acid disulphide by milling. This material may be stored or manipulated substantially without the occurrence of vulcanization therein. The benzaldehyde reacts with natural or casual amine in the rubber. The reaction product is preferably left in the rubber. hen it is desired to bring about vulcanization the compound is placed in a chamber and exposed to aniline vapor at a temperature of 140 F. for 1% hrs. at the end of which time vulcanization is accomplished.

Instead of thetreatment with aniline vapors to accomplish vulcanization the compound ma be immersed in a saturated aqueous solution of aniline for 12 hrs. and subsequently maintained at 2'12"v F. in water or in air for 1 hr.

Instead of the treatment with aniline vapor to accomplish vulcanization a treatment with diethylamine vapor may be employed. In this case an amount of rubber is treated with an amount of diethylamine equivalent to 0.5% of the weight of tile rubber.

Instead of treating the compound with aniline, diethylamine or the like thus replacing the ingredient whose vulcanizing function has been checked, heat alone may be employed. In carrying out the heat treatment the compound whose vulcanization has been checked by treatment with benzaldehyde as above is placed in a chamber and maintained at a temperature of approximately 266 vulcanization is accomplished. It will be observed that the quantity of benzaldehyde may be varied as desired, and in general it has for 1 hr. attheend of which time been observed that the larger the quantity of benzaldehyde employed the more slowly vulcanization occurs at any temperature. If

r it is found for example that prevulcanization occurs in the milling of a compound containing any given amount of aldehyde the addi tion of a further amount will avoid'prevulcanization. Thereafter if aniline or other amine is combined with the compound vulcanization is caused with the usual rapidity as soon as the effect of the aldehyde has been counteracted. I

It will be noted that various steps and processes set forth in my copending application Sr. No. 441,691, filed Feb. 1, 1921 may be used in conjunction with the present in vention.

The following is an illustration of the invention, wherein the aldehyde is introduced by diffusion, 100 parts of rubber containing natural or casual amine, 2 parts of zinc oxide, 2 parts of sulphur'and 2 parts of oxy normal butyl thiocarbonic acid disulphide is maintained over night in a receptacle of appropriate size to which has been added an amount of formaldehyde equal to 0.01 part of the weight of the rubber being treated. Formaldehyde is preferably introduced in the gaseous form which may be produced in any desired manner. If large amounts of rubber and large receptacles are employed it is necessary to circulate the gases in order that all of the rubber may be exposed thereto, Since the formaldehyde penetrates the rubber in order to react with the amine, it is desirable that the rubber be exposed thereto in thin sheets, say 0.1 inch or less in thickness although other thicknesses may be employed if desired. After treatment with formaldehyde the gas is blown out of the receptacle and the treated rubber aerated in a current of air until the odor of formaldehyde, is lost. The treatment just given retards the vulcanization of the compound. Thereafter vulcanization may be resumed by placing the rubber in a receptacle containing aniline vapor heated to 140 F. for 14 hrs; whereupon vulcanization is completed. The Various methods mentioned under the first example may be employed here if desired.

Rubber obtained by spraying whether in the form of rubber sponge or in compressed form in thin sheets, say 0.1 inch in thickness is treated for 12 hrs. with 0.05 of its weight of formaldehyde. The formaldehyde penetrates the rubber and reacts with any remaining ammonia or primary amine. The ammonia or primary amine if present intoo large an amount tends to decompose certain disulphide accelerators, such as oxy normal butyl thiocarbonic acid disulphide. Thereafter 100 parts of such rubber are combined with 2 parts of oxy normal butyl thiocarbonic acid disulphide, 2 parts of zinc oxide, 2 parts of sulphur andvulcanized by any of the methods set forth above.

If desired an aldehyde, which due to the fact that it exists as aliquid at ordinary temperature and is therefore not so apt to leave the rubber as formaldehyde, may be 1ntroduced into the rubber. Such an aldehyde'is benzaldehyde. It may be introduced as follows: 100 parts of rubber which may contain casual amine or which may subsequently absorb a casual amine are mixed with 2 parts of zinc oxide, 2 parts of oxy normal butyl thiocarbonic acid disulphide and 2 parts of sulphur. This compound preferably in the form of masses of approximately 0.1 inch thickness or less is maintained over night in a receptacle containing benzaldehyde liquid whose vapors at ordinary temperature are distributed about the receptacle and penetrate the rubber mass, reacting with any casual amine already present. Thereafter the rubber so compounded is removed and a quantity of benzaldehyde remains therein so that any casual amine that may come in contact with the rubber will be neutralized by the benzaldehyde present. The vulcanization of the compound is accordingly retarded. vulcanization may be resumed by placing the compound in a receptacle containing aniline vapor heated to 140 F. for 14 hrs. whereupon vulcanization is completed. Any of the procedures mentioned under the first example may be used. Amounts of aldehyde are employed to permit absorption by the rubber of a sufficient amount to react with the amine, with an excess remaining at the end of the period of exposure.

The process may also be carried out by using vulcanized rubberresulting from the vulcanization of a compoundmade up from 100 parts of rubber, 10 parts of zinc'oxide, 2 parts of dibenzylamine and 6 parts of sulphur vulcanized by treatment with the mixed vapors of carbon disulphide and carbon tetrachloride at 180200 F. as disclosed in my application Serial No. 574,797, filed July 13, 1922, now Patent No. 1,463,794. 0 After treatment with carbon disulphide and carbon tetrachloride as indicated the vulcanized rubber is treated with 0.01 part of its weight of formaldehyde as described above. Without such treatment the compound will continue to vulcanize until practically all six parts of the sulphur have combined with the rubber thus producingan over-vulcanized product. By the process given vulcanization is substantially retarded and over-vulcanization of the material is reduced.

Instead of oxy normal butyl thiocarbonic acid disulphide mentioned in any of the above examples, the following vulcanizing ingredients may be substituted to be treated by the processes before mentioned herein:

Zinc butyl xanthogenate, thiobenzoylmonosulphide, oxy ethylthiocarbonic acid disulphide and zinc 'dithiobenzoate' in compounds or cements. The proportion ofeach of these materials preferably employed is as follows: 100 parts of rubber, 10 parts of zinc oxide, 3 parts of sulphur and'fromOl to 3 parts of the zinc butyl Xanthogenate, thiobenzoylmonosulphid'e, oXy ethylthiocarbonicacid disulphide or zinc dithiobenzoate.

It will be Observed that oXy normal butyl thiocarbonic acid disulphide, zinc dithiobenzoate, .zinc butyl Xanthogenate, thiobenzoylmonosulphide, oxy ethylthiocarbonic acid disulphide are representatives of a large class of materials whose action may be controlled in a manner similar to that above set forth. This class of materials includes thiol salts, disulphides and monosulphides some of which are set forth in my Patents 1,440,962, 1,440,963, 1,440,964, 1,440,961, and my copending applications Sr. Nos. 548,828, 548,- 829,548,831, now issued as U. S. Patents 1,532,226, 1,532,227 and 1,510,652 respectively. In the patents herein mentioned and in general where it is desired to control the vulcanization of rubber by chemically treating vulcanizing ingredients or particularly where it is desired to control the vulcanization of rubber containing sulphur and amine, zinc or equivalent metal, carbon disulphide or materials containing the group 0 s ll where X represents sulphur or a'substitute Y element or group the processes herein set forth may be employed.

The processes herein set forth are simple and efficient. They cause either partial or complete stoppage of vulcanization when applied to the various types of rubber employed containing one or more vulcanizing. ingredients. They permit easy resumption of vulcanization later, if desired. Furthermore a uniform rate of vulcanization may be established for different lots of raw rubbers such as smoked sheet by the processes described. The products resulting from the process may be manipulatedwithout fear of premature vulcanization and as a result the difficulty of'producing scrap rubber in factory operations which vulcanized before it-could be reformed into articles and which represented accordingly a losshas been done away with. Products in which over-vulcanization has been prevented by the processes herein included have a correspondingly increased resistance to ageing.

Having thus described my invention, what I claim and desire to protect by Letters Pa tent is:

1. A process-for controlling the vulcanization of rubber containingv sulphur, amine, metal in combination, and amaterial containing carbon disulphide, whichcomprises causing the amine contained. in rubber to re act with an aldehyde to check the usual vulcanizing action on the" rubber of the amine, treating the rubber with a quantity of'amine, and vulcanizing the rubber.

2. A process for controlling the vulcanizav tion of rubber containing sulphur, amine, metal in combination, and a material containing carbon disulphide, which comprises causing the amine contained in rubber to react with benzaldehyde to check the usual vulcanizing action ;on the rubber of the amine, treating the rubber with a quantity of amine, and vulcanizing the rubber.

3. A step in the process of controlling the vulcanization of rubber containing sulphur, amine, metal in combination, and a-material containing carbon disulphide, which comits 

